Posted
by
samzenpus
on Monday June 13, 2011 @07:08AM
from the no-new-particle-for-you dept.

"Back in April physicists at Fermilab speculated that they may have discovered a new force or particle. But now another team has analyzed data from the collider and come to the exact opposite conclusion. From the article: 'But now, a rival team performing an independent analysis of Tevatron data has turned up no sign of the bump. It is using the same amount of data as CDF reported in April, but this data was collected at a different detector at the collider called DZero. "Nope, nothing here – sorry," says Dmitri Denisov, a spokesman for DZero.'"

What about this comment [slashdot.org] on the original/. post:
D0 has done this same sort of analysis, and they do not see this bump. But, their background modeling procedure involves reweighting the expected distributions (from Monte Carlo) in delta R between the jets (sort of an angular separation between the jets), which is a variable that is strongly correlated with the dijet mass. That is, their background model would be expected to have a strong tendency to fill in a bump like this. Now, which model is more correct is open to question, but it is certainly true that whether or not this bump turns out to be from real new physics (unlikely, in my professional opinion), their procedure is almost guaranteed not to find it.

That was me. In the analysis released on Friday, D0 does not perform the delta R reweighting (this was a specific criticism that they sought to address). In spite of no delta R reweighting, they still do not see the bump. There are some systematic errors that they handle differently from CDF which are quite likely to explain the result. Some of my colleagues at CDF are investigating (and were investigating before this D0 release, because of a suggestion by a D0 physicist at the release of the original bump paper) these systematics and their effect on our ability to model the data well. I can't really comment further until results are released, however.

Ex particles guy writing here --- the reason that data isn't immediately shared is that data acquisition and first pass analysis have to be done before you even *think* about looking for new physics. Moreover, the detector systems are complex enough, that it is really hard to be sure the analysis works correctly when you were the one who built the bleedin' thing. Then there's the other half -- almost no detector has complete coverage -- certainly none of the detectors at FNAL or CERN do so you are at the mercy of Monte Carlo simulations to work out the corrections. So you have to do the experiment twice; once is the physical world and once in a virtual world. Mismatches between the worlds can easily lead to spurious signals. Not saying that astronomy is any easier -- at least as its practiced now a days. And WMAP, for example, doesn't seem to be giving away the raw data. There is some turf protection -- "we invested blood sweat and tears as well as years of our lives to build the detector -- we get first crack at the data" -- I don't think that's a bad thing.

The particle physics community does have the equivalent of a star map it's the Review of Particle Properties (RPP).